[WIP] Add simple architecture diagram

[yuvipanda]

The diagrams package lets us create nice, graphviz
based diagrams from python.

[yuvipanda]

Need to figure out where to include this in the docs

[consideRatio]

1. The SFTP k8s service expose a port with name ssh and number 22 (Recent change by me from number 2222)
2. The SFTP k8s service targets a port with the name ssh on the pod (Recent change by me from targeting port 2222 by number rather than name)
3. The SFTP k8s pod expose a port with name ssh and number 2222

Services can have sensible numbers <1000, pods should stay above 1000 though to comply with pod security policies etc.

Suggested change

	sftp = autohttps >> Edge(label="port 2222") >> Deployment("jupyterhub-sftp")
	sftp = autohttps >> Edge(label="port 22") >> Deployment("jupyterhub-sftp")

[consideRatio]

It would be good to clarify this is assuming we have deployed jupyterhub ssh alongside z2jh.

[consideRatio]

❤️ wieeee more diagrams! :D This is a very helpful diagram!

Questions raised when I viewed it (here):

• What does a red line mean? It means SSH traffic right? Let's make the line between autohttps and jupyterhub-ssh red as well. And the one from autohttps to SFTP perhaps.
• What does "start server if needed" refer to? It would be good to clarify that the jupyterhub-ssh server does this via REST if needed.
• Perhaps a dedicated color for HTTP traffic, or somehow make it clearer that the storage is mounted to the pods rather than for example SFTP sending SSH/HTTP traffic further along to the user storage.

[GeorgianaElena]

😍 Such a nice diagram! I think it would be really useful to have it somewhere super visible, like the README.